Hi ynorma29,

Sales created before the GST registration is referred to as regular invoices/sales receipts.

Here's how to record them in your QuickBooks Online:

1. Click on the Plus icon.
2. Choose Invoice or Sales Receipt.
3. Select a customer, enter the item details, and amount.
4. In the Amounts are drop-down, select Out of scope of GST. 
5. Click on Save and close.

This is an example screenshot:

You can also read more of this rule from the Department of Industry's website: https://www.business.gov.au/finance/payments-and-invoicing/types-of-invoices

Is your GST setup not yet complete? This reference will be a great guide for you: How to setup GST in QuickBooks Online?

Keep us posted if you have questions about GST or anything else. We're here to help.